Various types of wheel mechanisms exist for strollers, shopping carts, gurneys and the like. A common drawback to the designs is maneuverability, particularly on uneven ground. Existing wheel mechanism designs include single wheels at each of the four corners of a cart, stroller, or other mobile unit that rotate on a front and rear axle that span the width of the unit. The front wheels, and sometimes the back wheels also can pivot from right to left with respect to forward and reverse movement of the unit, and vice versa, to facilitate turning. This is the type of wheel device used in automobiles, trucks, buses, etc.
Strollers and other carts often have separate wheel mechanisms for each of the four corners of the device. Each separate mechanism has a wheel that rolls forward or backward and also pivots about an axis for ease of turning. These mechanisms work well on level surfaces, and thus are appropriate for use on a shopping cart in a market or a gurney in a hospital, etc. but do not function as well on uneven surfaces or in small spaces. Additionally, these mechanisms have limitations even on smooth surfaces, such as a decrease in maneuverability associated with large or uneven loads. Accordingly, there is a need for a wheel mechanism that can be used on uneven surfaces, such as that which is found outdoors, up and down steps, or where a small turning radius is beneficial. Further, there is a need for improved maneuverability when carrying large or uneven loads.